The use of carbon disulfide for dewaxing paraffin deposits in oil and gas wells is known in the art. Carbon disulfide has proven effective for this purpose due to its unique ability to solubilize even the most difficult of paraffins. For example, carbon disulfide is able to solubilize paraffins containing 20-30 or more carbon atoms, as well as up to 50% of its weight in sulfur.
However, the use of carbon disulfide in dewaxing oil and gas wells has fallen under disfavor in the oil and gas industry due to safety concerns. Among these safety concerns is the fact that carbon disulfide has a flash point of -30.degree. C. and an autoignition temperature of only 125.degree. C. Accordingly, if a carbon disulfide solution were to be used in the vicinity of an open flame or an ignition source, ignition would be likely. Moreover, carbon disulfide is highly toxic, and exposure thereto may lead to neurological damage. In view of these factors, the oil and gas industry has attempted to avoid carbon disulfide use.
In light of the inherent dangers of carbon disulfide, research has been conducted to attempt to reduce the hazards associated with its use. Generally, these methods have addressed the autoignition temperature of carbon disulfide. However, none has effectively addressed the flammability problems.
For example, U.S. Pat. No. 3,298,907 discloses a blend of carbon disulfide and chlorofluorocarbons which raises the autoignition temperature of carbon disulfide. Although these blends have proven effective in raising the autoignition temperature of carbon disulfide, they have no effect on the flash point thereof. Also, these blends are costly and environmentally dangerous due to the excessive chlorofluorocarbon (15-60 percent be weight) and methylene chloride (20-60 percent by weight) content.
Further attempts have been made to raise the autoignition temperature of carbon disulfide through the addition of various other hydrocarbons. For example, U.S. Pat. No. 3,375,192 discloses a method whereby 4 to 16 percent by weight of pentane is added to a carbon disulfide solution to raise the autoignition temperature from 115.degree. C. to 357.degree. C.
Also, it has been discovered that light alkenes, such as isoprene, are effective in raising the autoignition temperature of carbon disulfide (see J. B. Hyne and J. W. Greidanus, Canadian Journal of Chemical Engineering, 48 (4) pp. 471-473 (1970)). Specifically, the use of isoprene at a concentration of 5 percent by weight, was found to raise the autoignition temperature of carbon disulfide to higher than 300.degree. C.
In U.S. Pat. No. 3,644,433, it was disclosed that a mixture of carbon disulfide and 5-40 percent of cracked or coke naphtha containing significant amounts of unsaturation significantly raised the autoignition temperature of carbon disulfide.
Another method for raising the autoignition temperature of carbon disulfide comprises blending the carbon disulfide with organo-sulfur chemicals. For example, U.S. Pat. No. 3,558,509 described in examples that the addition of 0.1-1.0 percent by weight of dimethylsulfoxide, alkylsulfides or disulfides (having an alkyl chain length of up to 5 carbons) to carbon disulfide elevates the autoignition temperature of the carbon disulfide to greater than about 150.degree. C.
It is also known that the addition of halogens or ethanol to carbon disulfide effectively raises its autoignition temperature. For example, U.S. Pat. No. 3,558,510 discloses that the use of one percent by weight of iodine or bromine or six percent by weight of ethanol raises the autoignition temperature of carbon disulfide to greater than about 150.degree. C. However, the use of halogens in oil an gas well applications has fallen upon disfavor, due to the significant corrosion problems associated therewith.
Further attempts to adjust the autoignition temperature of carbon disulfide include the use of emulsions. For example, U.S. Pat. Nos. 3,700,594 and 3,732,166 disclose that non-Newtonian microemulsions of carbon disulfide in water have a higher autoignition temperature than carbon disulfide solutions alone. The use of such emulsions for treating oil and gas wells is also disclosed. Although such emulsions have been shown to decrease the flammability of carbon disulfide solutions, they have proven to be unstable, i.e. phase saturation occurs upon long-term storage.
However, these references do not recognize that carbon disulfide mixtures also have very low flash points. For example, n-pentane has a flash point of -40.degree. F. (see U.S. Pat. No. 3,375,192). The flash point is the temperature at which ignition occurs with an open flame. The ignition temperature is always much higher than the flash point, since it measures temperatures at which the vapor mixed with air will ignite on a hot surface.
In view of the failure of these attempts to produce carbon disulfide compositions which may be handled without the inherent dangers of ignition described above, a method for the in situ production of carbon disulfide would be valuable.
In addition to the inherent dangers of ignition possessed by carbon disulfide solutions, another disadvantage of handling free carbon disulfide is its toxicity. A method for the in situ production of carbon disulfide would be advantageous in that it would avoid the toxic exposure of workers handling free carbon disulfide.
Sodium tetrathiocarbonate and other members of the thiocarbonate family are known to generate carbon disulfide under certain conditions. For example, U.S. Pat. No. 3,400,104 discloses the use of this salt in the synthetic preparation of various polymeric organic carbon disulfides. French Patent 1,540,473 discloses the use of peroxythiocarbonates as polymerization inhibitors. However, the use of these salts for the in situ generation of carbon disulfide, particularly in a method for dewaxing oil and gas wells, has been heretofore unknown in the art.
It can be seen that there is a need for a method of dewaxing oil and gas wells and pipelines which will allow for the safe use of carbon disulfide.